Top Menu Drop Down Not Covering Whats Underneath

I have placed a category block in the left column at the top under the horizontal menu but when I hover over the horizontal menu the drop down does not cover whats underneath so all the text is mixed together.

The drop down seems to cover other elements.

I have shown this in the attached pictures. Any ideas on how to fix ??




I have now posted this as a bug report

Fix and Explanation


I think you need to increase the z-index of the top menu to more than 501